A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. The following notice applies to the software and data as described below and in the drawing hereto: Copyright(copyright)1999, Libit Signal Processing, Ltd., All Rights Reserved.
The present invention relates generally to communication methods and systems and in particular to communication methods and systems implemented using CATV (Cable Television) systems.
Cable television (CATV) systems were originally intended to deliver analog television signals to homes in an essentially unidirectional manner. However, the coaxial cable used to carry these signals can support bidirectional transmission of signals, i.e., transmission both to and from the home. As a result, cable television companies have begun to provide data communications services to meet consumers"" growing demand for high speed data transmission over computer networks, such as the Internet.
Devices known as cable modems have been developed to convert digital data to a modulated radio frequency (RF) signal, and vice versa, for transmission on a CATV system. This conversion is performed both by a cable modem at the subscriber""s home and, on the other end, by headend equipment handling multiple subscribers. Thus, the subscriber receives data from a computer network using a downstream channel and transmits data to the network using an upstream channel.
As computer networks deliver increasing amounts of content to users, a need has arisen for increased throughput and communications robustness. It is also essential that communications equipment operate over a wide range of channel impairments, which can include, for example, ingress noise, burst noise, impulse noise, linear distortions, non-linear distortions, and adjacent channel interference. Moreover, the different types of services that use CATV systems give rise to additional needs. For example, for data services, such as Internet access, a high packet throughput and a low packet error rate are primary considerations. For such applications, low delay is not a key consideration. For multimedia services, such as speech, video, and telephony, however, low delay is the primary consideration. It is desirable to minimize the periods of a high bit error rate (BER) for these applications. Additionally, compatibility with existing standards and equipment is important for all applications.
According to one embodiment of the present invention, a transmission arrangement is used for transmitting a data signal using a cable television transmission medium. An encoder encodes an input data stream as an encoder output signal. Adjacent channel interference in this signal is then reduced using a transmission filter arrangement, thereby generating a filter output signal. A modulator modulates the filter output signal to generate a modulated radio frequency signal for transmission using the cable television transmission medium. Another embodiment is directed to a communication system that, in addition to the above, includes a receiver arrangement that generates a stream of detected data based on the received modulated radio frequency signal.
Yet another embodiment of the present invention is directed to an analog front end arrangement for use in the communication system. The analog front end arrangement comprises a plurality of band pass filters coupled to receive a modulated radio frequency signal. Each of the band pass filters is centered around a different frequency. The sample rate is less than the Nyquist rate so as to cause aliasing deliberately. A multiplexer receives output signals from the band pass filters and couples a selected one of the band pass filter output signals to an output of the multiplexer. An analog to digital converter provides a digital signal, generated as a function of the output of the multiplexer and a clock signal, to a digital receiver. Sample rate logic provides, as a function of the center freqeuency, a select signal to the multiplexer, a rate parameter to the clock signal generator, and a spectrum inversion indication to the digital receiver.
Other embodiments are directed to methods for transmitting or communicating a data signal using a cable television transmission medium.
Another aspect of the present invention provides methods and arrangements for robust communications over noisy communications channels using data retransmission and/or diversity techniques. In one particular embodiment, a communication arrangement includes an encoder that reproduces a symbol or FEC block represented by a segment of an input data stream a predetermined number of times. A transmission arrangement having a plurality of transmission channels transmits each reproduced symbol or FEC block using a distinct transmission channel. A receiver performs soft-combining of signals received from the outputs of the transmission arrangement.
The present invention can be implemented in full compliance with current network specifications and/or on top of the existing specifications in a manner that enables co-existence of advanced modems designed according to the present invention with current modems.